Strain-tide spectroscopy

Summary. We have used two years of strain-tide data to study the response of the Earth to the diurnal and semidiurnal tidal excitations. Our results show that there is significant structure in the response of the Earth to tidal excitations near one cycle/sidereal day. This structure agrees with the resonance behaviour predicted from calculations of the forced elastic-gravitational response of an elliptical, rotating earth with a liquid outer core. The data can also be used to test for possible preferred frames and spatial anisotropies. We find that upper bounds on the parameterized post-Newtonian (PPN) parameters which characterize these effects are α₂≤ 0.007 and ζ_w≤ 0.005. We also infer that there is a significant frequency dependence to the ocean load near one cycle/day and that the coherence between strain and barometric pressure fluctuations are significant at periods longer than a few days.